Grinding machine



1951 H. B. DUNCAN 2,566,059

GRINDING MACHINE Filed Feb. 25, 1949 3 Sheets-Sheet 1 1 I E1 1; INVENTOR.

Hersbe/ 5. Duncan BY ATTOIQVEYS' Aug. 28, 1951 H. B. DUNCAN 2,566,059

GRINDING MACHINE Filed Feb. 25, 1949 3 Sheets-Sheet 5 IN VEN TOR. fiersfie/ 5. 00/760 Patented Aug. 28, 1951 GRINDING MACHINE Hershel 13. Duncan, Detroit, Mich., assignor to General Electric Company, a corporation of New York Application February 25, 1949, Serial No. 78,286

6 Claims.

This invention relates to a grinding machine for grinding balls and more particularly to a machine for grinding balls consisting of pressed powdered ingredients, and in particular unsmtered pressed balls of powder ingredients used in the manufacture of refractory metal carbides such, for example, as tungsten carbide, titanium carbide, tantalum carbide, molybdenum carbide, cobalt and nickel powders.

This invention contemplates a grinding apparatus which will grind such pressed powder balls efficiently and automatically to precise predetermined diameters.

It is also an object of this invention to produce a grinding machine for efficiently grinding pressed metal powder balls which is of simple structure, dependable in operation, and which requires a minimum amount of attention on the part of the operator.

Referrings to the drawings:

Fig. 1 is a perspective view of the grinding machine embodying the features of my invention;

Fig. 2 is a plan view of the grinding wheels and the ball to be ground.

Figs. 3 and 4 are diagrammatic views illustrating the automatic operation of the grinding machine.

Fig. 5 is a perspective view of another and preferred form of a .grinding'machine embodying the features of my invention.

Fig. 6 is a top plan view showing the grinding wheels and one of the balls being ground.

Fig. '7 is a vertical section through the grinding wheels taken in the plane of the Wheels and showing the air jet and one of the balls being ground with the air jet directed downwardly.

Fig. 8 is a perspective View of the rotating plate.

Fig. 9 is a vertical section through the grinding wheels taken in the plane of the wheels and showing the air jet and one of the balls being ground with the air jet directed upwardly.

Fig. 10 is a top plan view of the grinding wheels and the ball to be ground showing two different angular positions of the grinding wheels.

Fig. 11 is a horizontal section through the grinding wheels taken along the line llll of Fig. '7.

Fig. 12 is a section taken along the line l2l2 of Fig. 5.

Fig. 13 is a section taken along the line I3l3 of Fig. 5.

My improved grinding machine comprises two grinding wheels i and 2 mounted on shafts 3 and 4 respectively and rigidly held in position thereon between steel plates 5 and 6. Shafts 3 and 4 are supported in similar bearings 'l which in turn are supported on similar pedestals 8 each of which are integral with a base plate 9. The grinding Wheel 1 may be adjusted to occupy any desired position in relation to grinding wheel 2 by loosening a bolt I!) which normally holds the base plate 9 rigidly in position.

The diameters of grindings wheels I and 2 are substantially equal and their peripheries are grooved or rounded on a radius to form equal portions of a toric surface as indicated at H and I2 in Fig. 2. Prior to the grinding operation, wheels I and 2 are adjusted until the wheels are, e. g., substantially at right angles to one another with the outer edges I3 and I 4 of curved surfaces II and I2 almost but not quitein contact, as indicated in Fig. 2 of the drawing. As thus positioned, the rounded portions II and 12 of the grinding wheels form a circular opening having a radius slightly greater than that desired in the ground balls.

The adjacent rounded surfaces on the grinding wheels rotate upwardly, as indicated by the arrows on wheels and 2, and preferably at the same speed and may be driven by separate motors or by means of an electric motor 15 driving a shaft !6 which in turn drives pulleys l1 and [8 located respectively on shafts 3 and 4.

The balls or pellets to be ground may be formed from the powdered ingredients to approximately the desired shape in a pill press machine but such balls are not perfectly spherical. When a ball to be ground is dropped between the rotating grinding wheels it remains there until it is ground to a radius substantially equal to or slightly less than the radius of curved surfaces H and i2 at which time it drops through the circular opening between them and into a receptacle l9. Thereafter the ground ball may be sintered in a manner well known in the art.

To provide for automatic operation of the machine the balls 20 to be ground are placed in an inclined slightly V-shaped metal trough 2| and normally held from downward movement thereon by means of a tubular or gate 22. The tumbler may be turned in opposite directions through an arc of and its operation is controlled by the ball which has been ground to a desired or predetermined diameter between the grinding Wheels.

The tumbler has two fiat surfaces 23 and 24 disposed "at right angles to one another and adapted to accommodate one ball in the angular space thus provided.

The troughs 2| extends to a point directly over the circular opening between the grinding wheels I and 2 and is sharply inclined downwardly at its lower end so that when a ball 20 rolls down the inclined surface of the trough 2| it will drop between the cooperating grinding surfaces II and [2. The ball is then ground therein to a predetermined diameter at which time it will drop through the opening between the grinding wheels and strike the slightly curved end portion of a trip pedal 25 positioned directly below the opening. To prevent damage to the ground pressed powder ball a felt or rubber pad 26 is placed beneath the trip pedal.

The trip pedal is pivoted intermediate its length and a mercury switch 21 is attached to the trip pedal and operable therewith. While a ball is being ground the mercury switch occupies a position in which a circuit is completed from a source of power through wires 28 and 2:9, switch 21', and solenoid 30 which is thereby energized to hold its metal core 3! in the position indicated in Fig. 3. When a ground ball drops through the opening between the rounded surfaces H and I2 and strikes trip pedal 25 the pedal and mercury switch are depressed to the position indicated in Fig. 4 thereby opening the mercury switch and power supply circuit and deenergizing solenoid 35. At the same time the ground ball will roll off the depressed trip pedal and drop onto the pad 26 in basket 19.

Core 3| of solenoid 30 is mechanically connected to tumbler 22 by a system of levers 32. When solenoid 30 is energized, the tumbler 22 and levers 32 occupy the position indicated in Fig. 3. However, when the solenoid is deenergized the core 3| drops to the position indicated in Fig. 4 and thereby moves the tumbler 22 to the position indicated in Fig. 4 thereby permitting a ball 25 to be dropped between the grinding Wheels I and 2. The tumbler meanwhile acts as a gate to prevent dropping more than one ball at a time between the grinding wheels.

Trip lever 25 is provided with a counterweight 33 which may be adjusted to various positions depending upon the weight of the ball being ground. When a ground ball rolls oil the end of the trip lever the counterweight 33 brings lever 25 back to the position indicated in Fig. 3 in which the mercury switch is again closed and the solenoid 29 energized to raise the core 3!. At the same time levers 32 and tumbler 22 are operated by the movement of the core 3| and moved to the position indicated in Fig. 3.

In the automatic operation the operator is merely required to place the balls to be ground in the trough 2|. It will be understood of course that grinding wheels may be employed having grooved portions of various radii to accommodate different sizes of balls to be ground.

In the grinding operation the ball or pellet to be ground appears to float between the grinding wheels. Since the adjacent grinding surfaces rotate in an upward direction they tend to lift the ball upwardly while gravity, of course, exerts a pull in the opposite direction. This lifting action of the grinding wheels imparts an ever changing, centerless, rotating, restless motion to the ball being ground. Since the article to be ground is not held or supported in position it is believed that the present method of grinding may properly be designated restless grinding.

My prior copending application Serial No. 585,956, filed March 31, 1945 (now abandoned), of which this application is a continuation-inpart, shows and describes the form of my invention shown in Figs. 1 to 4 inclusive. Since gravity is relied upon during grinding to maintain the ball in grinding relation with the wheels, the degree of floating is dependent upon the weight of the ball and the speeds of the rotating wheels. In using the above described grinding machine, Figs. 1 to 4, for grinding small balls having diameters of approximately threeeighths of an inch and less, the productive capacity of this machine has been lowered due to excessive floating and even expulsion of the balls from the concave surfaces of the grinding wheels due to insufiicient weight of the balls to return them to the grinding surfaces. Decreasing the speed of rotation of the grinding wheels is not a practical solution to the problem of excessive floating since the decrease in the speed of the grinding wheels also decreases the efficiency and productive capacity of the grinding machine greatly. Although the above described machine is operable and will satisfactorily grind balls of pressed powdered ingredients commonly used in the manufacture of refractory metal carbides, in Figs. 5 through 13 I have shown an improved form of grinding machine which will grind various sizes of such balls with greater efiiciency than the above described form of my invention.

Referring to Fig. 5, my machine comprises grinding wheels 4| and 42 mounted on shafts 43 and 64, respectively, and rigidly held in position thereon between steel plates 45 and 45 (Fig. 6). Shafts 43 and 44 are supported in similar bearings 4'! which in turn are supported in housings 48 and 49 each of which are integral with base plate 55. Housing 48 is mounted on a universal head so that the grinding wheel I may be adjusted to occupy any desired angular position in relation to grinding wheel 42 by adjusting screws 5| and 52.

The diameters of grinding wheels 4| and 42 are substantially equal and their peripheries are grooved or rounded on a radius to form equal portions of a toric surface as indicated at 53 and 54, Figs. 6, 11.

While grinding wheels (I and 2 and 4! and 42) may be disposed at right angles to each other, Figs. 1, 2, or angularly disposed at 180, Figs. 5, 6, the included angle between the wheels, that is, the included angle between the planes of the wheels can be substantially less than or can be increased to the extreme limit beyond 90 whereupon the wheels are angularly disposed at or in line with relation to each other, Fig. 5. It is important that the wheels should rotate preferably in a vertical plane although the wheels can be tilted a few degrees on either side of the vertical plane. Whatever the angular relation of the grinding wheels, the arcuate grooves on the peripheries of the wheels should preferably be opposed to each other so that they contact the ball being ground on opposite sides.

Before the grinding operation, preferably Wheels 4| and 42 are adjusted until the wheels are angularly disposed at 180 or in line with relation to one another so that the rounded portions 53 and 54 form a circular opening having a radius slightly greater than that desired in the ground balls.

The adjacent rounded surfaces on the grinding wheels rotate upwardly, as indicated by the arrows on wheels 4| and 42 and at the same, or at different speeds, preferably the latter. The wheels may be driven by separate motors or by one motor connected by a belt drive with pulleys 55 and 56, pulley 56 having a larger diameter than pulley 55 which gives wheels 4| a greater angular speed than wheel 42.

To reduce the floating of small balls during grinding, I have provided an air jet or nozzle 51 supplied with air under pressure from pipe 58 through line 15 with the discharge being reg ulated by valve 59. When a small ball to be ground is dropped between the rotating grinding wheels, the stream of air discharged from jet 51 directed downwardly between the wheels and against the ball decreases its amplitude of floating so that it remains against the Wheels until it is ground to a radius substantially equal to or slightly less than the radius of curved surfaces '53 and 54 at which time it drops through the circular opening between them into a receptacle 60.

The air jet also increases the efficiency of grinding on pressed powder balls larger than approximately diameter and up to approximately diameter. On balls consistingof pressed power constituents having diameters greater than approximately and less than approximately the use of the air jet is not particularly necessary, but on balls larger than approximately in diameter, most efficient grinding results when the air jet 5! is located beneath and between the wheels so that the upward discharge of air or other gas from jet 5! tends to lift the ball 6| being ground and to increase the floating action. It is to be understood that the above imposed limits relate to balls made of pressed powder ingredients used in the manufacture of refractory metal carbides having a density between about 6 g./cc. and about 11 g./cc. in the pressed state, and that they are given for exemplary purposes only. These powdered ingredients, as is well known, consist, for example, of tungsten carbide, molybdenum carbide, titanium carbide, tantalum carbide, and binder metals of the iron group, such as nickel and cobalt.

To provide for automatic operation of the machine, the balls 6| are placed in an inclined rounded hopper 52 having at its lower end a loading plate 63 mounted on inclined shaft 64 and rotated by motor .65 through the variable speed drive 66. Loading plate 63 has on its periphery three equally spaced similar ball pickup recesses 61, and a thickness corresponding to the diameter of the ball to be ground. Loadin plate 53 rotates within a cylindrical housing concentric with plate 63 and positioned closely adjacent the circumference of loading plate 63. The forward end of housing 10 is closed by plate H provided with an opening l2 through which the balls are fed from the loading plate, into the right hand end of inclined chute .68. The

speed of rotation of loading plate 63 is controlled 1 by regulating variable speed drive 66 so that loading plate 63 deposits a ball on inclined chute 68 just after the'previously ground ball drops into receptacle N). In the automatic operation, the operator is merely required to place the balls 5| to be ground in the hopper 62. Due to the inclination of hopper 62, the balls roll to the lower end of the chute 62 whereupon they are picked up one by one by the recesses 6'! in plate 63 and carried through the cooperation of housing 78, clockwise and upwardly until the recess 61 carrying the ball coincides with opening 12 whereupon due to the downward inclination of shaft 64, plate 63 and pick up recesses 61, the ball will roll by gravity from recess 61 through hole l2 into and down inclined chute 68 which deposits the ball to be ground between rotating wheels 4| and 42 in the position indicated in Figs. 6, 7 and 9. The speed of rotation of loading plate 63 is timed in accordance with the time required for the grinding wheels 4| and 42 to grind a ball to size and discharge the same so that the loading plate will cause a ball to be deposited in grinding position upon and between wheels 4| and 42 shortly after the previously ground ball drops -from'between the wheels into receptacle 66.

As stated above, the preferred angular relation of the grinding wheels is one in which they are aligned, that is, positioned in the same vertical plane to form a straight angle (180). However, in Fig. 10, Ihave illustrated other angular positions of my grinding wheels. It should be noted that the angular distance between the outer edges l3 of curved surfaces l2 or 53, 54 should always be less than 180 and thesame holds true with regard to the angular distance between the outer edges I 4 of said curved surfaces. Referring to Fig. 10 in the full line showing, the included angle between the wheels I and 2 is about and in the dotted line showing the included angle between the wheels is about 60, which is the preferred lower limit of this angular relationship between the wheels.

In -the dotted line showing of wheel 2, Fig. 10,

it will be noted that edges M of wheels I and 2 nearly contact whereas the angular distance between edges iii of wheels I and 2 will leave approximately one-third of sphere 6| unsurrounded and it is preferred that not more than about one-third of the sphere or ball 6| should be unsurrounded by the grinding wheels otherwise a point is reached at which the lack of support on opposite sides of the sphere is of such magnitude that the ball being ground tends to be kicked out and away from the grinding groove. Thegrinding wheels I and 2, 4| and 42 can be disposed with respect to one another at an angle fallingwithin a range of from down to approximately 60, the important point bein v that the corresponding edges I3 of the cooperating grinding wheels must diverge downwardly from the point at which the wheels are closest together (that is, the area in which the ball is located while being ground), and the same is true with respect to corresponding edges M of the two grinding wheels, so that the ball when finished ground will fall automatically by gravity from between the wheels.

It is to be understood that grinding wheels may be employed having grooved portions of various radii to accommodate different sizes of balls to be ground; that loading plates having varying thicknesses and varying sizes of pickup recesses may be employed; and that pairs of wheels may be mounted in'tandem to produce a production machine. The radii of grooves II and I2 are equal and the radii of grooves 53 and 54 are also equal. Further, the grinding wheels and 2, 4| and 42) come closest together at their circumferential edges in the plane passing through their axes of rotation and in this plane form an opening made up of two arcs of equalradii B (Fig. 11) which in substance can lie-considered a circular opening between the cir cumferential grinding surfaces of the wheels and through which the ball being ground cannot fall until finished to the size, or slightly less than the size, of this opening. It will be noted that in all'angular relations of the grinding wheels (Figs; 2, 6, 10) the concave grinding surface or periphery of wheel I or 42 is closely adjacent the concave grinding surface or periphery of wheel 2 or 4| as at 76 on one side of the axis (3) of rotation and that the concave grinding surface or periphery of wheel I or 42 on the opposite side of its axis of rotation as at 17 is further apart from the concave grinding surface on the other wheel 2 or 4|.

In a highly efficient version of my grinding machine for commercial production of balls or spheres of pressed powdered ingredients commonly used in the manufacture of refractory metal carbides as above specified, I have found that the preferred range of angular speeds of the grinding wheels at their grinding circumferences is between about 300 surface feet per minute and about 1000 surface feet per minute; the pressure of the air in line 58 may be to 60 pounds per square inch, however, the pressure here is of minor importance as long as the volume of air is plentiful and controllable by valve 59; the size of nozzle 51 may vary from about of an inch to about A; inch depending upon the size of the sphere being ground, with a inch diameter nozzle having proved entirely suflicient for all sizes of spheres; and the distance between the nozzle and the ball being ground may vary from 2 to 8 inches, with the most practical working distance being from 3 to 6 inches, and as long as the supply of air is sufficient this distance is not too critical.

I claim:

1. A grinding machine comprising two substantially vertically positioned rotatable grinding wheels each having a peripheral concave grinding surface extending circumferentially completely around the axis of rotation of said wheel and between which concave grinding surfaces a substantially spherical article may be ground to a predetermined diameter, mechanical means individually connected to and operable to drive said wheels in opposite directions so that the peripheral concave grinding surfaces rotate upwardly in the area of closest proximity whereby the grinding surfaces support and impart a lifting force to the article being ground, the curvatures of said circumferential concave grinding surfaces having substantially equal radii, said wheels being positioned with the periphery of the one wheel closely adjacent the periphery of the other wheel on one side of its axis of rotation and with the periphery of the one wheel on the opposite side of its axis of rotation further apart from the periphery of the other wheel whereby said concave surfaces cooperate in the area of closest proximity to form a substantially circular opening above which a substantially spherical article may be supported on both of said concave grinding surfaces and ground to a diameter slightly less than the diameter of said opening, said concave grinding surfaces providing the sole support for said article, and means for directing a substantially vertical gaseous stream between said concave grinding surfaces in the area of closest proximity whereby said stream impinges against the spherical article being ground.

2. The grinding machine claimed in claim 1 wherein the gaseous stream is discharged downwardly between said grinding surfaces.

3. The combination claimed in claim 1 wherein the gaseous stream is discharged upwardly between said grinding surfaces.

4. The grinding machine claimed in claim 1 wherein the stream of gas is directed downwardly when the diameter of the spherical article being ground does not exceed about /2 inch and wherein the stream of gas is directed upwardly when the diameter of the spherical article is about of an inch or more in diameter and wherein the above specified diameters of the balls are referred to spherical articles having densities fallferentially spaced pockets rotatabll mounted at the lower end of said hopper, a discharge outlet in the lower end of said hopper and positioned above the bottom of the hopper whereby as the elevator rotates the balls roll into said pockets and are elevated thereby to said discharge outlet through which they are discharged, the said rotary elevator being mounted upon a downwardly inclined axis about which said elevator rotates, the pockets in said elevator being open at opposite ends whereby the balls which roll from the hopper into one end of the pockets roll by gravity out of the other ends of the pockets as the pockets align one after the other with said discharge opening, and means for rotating the elevator at a uniform rate of speed whereby the balls are delivered to said discharge opening at a uniform rate.

6. A transfer mechanism for transferring spherical articles from one point to another at a predetermined rate comprising in combination an inclined hopper for the spherical articles which are to be transferred, a rotary elevator having a plurality of circumferentially spaced pockets rotatably mounted at the lower end of said hopper for rotation about a downwardly inclined axis, a discharge outlet in the lower end of said hopper and positioned above the bottom of the hopper whereby as the elevator rotates, the spherical articles roll into said pockets and are elevated thereby to said discharge outlet, said pockets being open at opposite ends whereby the spherical articles which roll from the hopper into one end of the pockets roll by gravity out of the other ends of the pockets as the pockets align one after the other with said discharge outlet, and means for rotating the elevator at a uniform rate of speed whereby the spherical articles are delivered to said discharge opening at a uniform rate.

HERSHEL B. DUNCAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,065,600 Euchenhofer et al. June 24, 1913 1,264,129 Reeves Apr. 23, 1918 1,819,308 Walker Aug. 18, 1931 1,846,661 Vuilleumier Feb. 23, 1932 1,871,866 Volz Aug. 16, 1932 2,041,764 Herrmann May 26, 1936 2,062,803 Benedek Dec. 1, 1936 FOREIGN PATENTS Number Country Date 81,491 Germany June 12, 1895 465,863 Germany Sept. 23, 1928 740,691 France Jan. 30, 1933 

